About the 1 H NMR Spectrum: The chemical shift values of this 1 H NMR spectrum h
ID: 960953 • Letter: A
Question
About the 1H NMR Spectrum:
The chemical shift values of this 1H NMR spectrum have been calibrated to the literature value of CHCl3present in CDCl3(7.26 ppm). The full spectrum is represented, followed by two zoomed in areas. Each signal on this spectrum has been labeled with a letter (A-F); however, some of these peaks belong to 2,3,4,5-tetraphenylcyclopentadienone, and others belong to one or more contaminants. The integrals for each peak are listed below, but they are relative ratios (not the number of H’s present), and the smallest aromatic peak on the spectrum has been arbitrarily assigned a value of 1.0.
About the 13C NMR Spectrum:
The chemical shift values of this 13C NMR spectrum have been calibrated to the literature value of CDCl3 (77.16 ppm). The full spectrum is represented, followed by one zoom. Each signal on this spectrum has been labeled with a letter (a-k).
1. 1H NMR Troubles. (2 pts) Even though this is a pure NMR spectrum of the listed compound, the NMR data are not easy to interpret. There are two (2) significant issues/problems/complexities that make a complete analysis of this spectrum impossible: briefly explain using a minimum of words.
2. 1H NMR Data. (6 pts) Given the hints listed below, process this 1H NMR data and transform it into text data that is appropriate for inclusion at the end of the Procedure. Here are the hints:
-Peak C in the 1H NMR spectrum corresponds to a single hydrogens type in the product that integrates to four hydrogens (4H); use this information to scale the other peaks accordingly.
-Each aromatic peak can be considered a multiplet (“m”), and there is no need to list or tabulate coupling information (J-values).
-Chemical shift (õ) values can be reported as an average of the centermost listed peaks, or as a range (most appropriate for peak A)
3. Extra H? What accounts for the “extra integral” (leftover H’s that are not part of the product) that you have uncovered in your analysis in Question 2.
4. 13C NMR Triumph. After the complexity of the 1H NMR data for this molecule, the 13C NMR spectrum is far more straightforward. Briefly state two (2) features of the 13C NMR data that clearly support the identity of the product.
5. 13C NMR Data. Using the supplemental handouts titled Reporting NMR and IR Data and NMR Product Data Format, process this 13C NMR data and transform it into text data that is appropriate for inclusion at the end of the Procedure.
6. Contaminants. Using this 1H NMR data, determine the identity and % composition of the contaminant compound(s) present in the spectrum. Justify your answer with pertinent chemical shift and splitting information.
Explanation / Answer
1.1H NMR Troubles:
i) Presence of undesired peaks at 1.253-1.288, 1.552 and 3.738-3.714 may cause problem in data analysis.
ii) The splitting patterns in aromatic regions are complex because of overlaping signals. So, to get the exact coupling constants (J values) for ortho, meta and para hydrogens are not convenient.
2. 1H NMR Data:
C: 6.941-6.965 (m, 4H, ArH)
B: 7.175-7.215 (m, 4H, ArH)
C: 7.255-7.272 (m, 12H, ArH)
3. Extra H:
Extra hydrogens belongs to the residual solvents and moisture (at 1.552 ppm for moisture) present in the sample.
4. 13C NMR Triumph:
i) Peak at 200.461 ppm belongs to C=O (carbonul functionality)
ii) Total number of signals (13) is showing the presence of symmetry in molecoles.
iii) Larger peaks represents ArCH carbons as compared to ArC carbons.
5. 13C NMR Data
13C NMR (100 MHz, CDCl3): 200.5 (CO), 154.6, 133.2, 130.9, 130.2, 129.5, 128.6, 128.2, 128.1, 127.6, 125.4 ppm.
6. Contaminants:
Integration ratio of peaks at 1.253-1.288 and 3.738-3.741 = 0.397 /0.0288 = ~1.4
The ratio of hydrogens in of CH3 and CH2 of CH3CH2OH = 3/2 = 1.5
The presence of a triplet at 1.253-1.288 and inegration ratio (~1.4) indicates the presence of CH3CH2OH as impurity.
So, Extra hydrogens belongs to the residual solvents CH3CH2OH and moisture (at 1.552 ppm for moisture) present in the sample.